Summary

Water in the right quality and quantity, and at the right time, is essential to life—for humans and their food crops, and for ecosystems. Millions of people yearly die of water-related diseases; floods and droughts also cause illness and death in addition to economic damage throughout the world. Much of our agricultural activity would collapse in the absence of irrigation water. Natural ecosystems are adapted to stream discharge, precipitation, and evaporation patterns. Thus, future adjustments in the water cycle to climate, weather, and land-use change will undoubtedly have complex and significant impacts on humans and other species that depend on it.

THE CHALLENGE OF UNDERSTANDING WATERFLOWS AND STORES

The management of water resources to meet these challenges will require improvements in our capacity to understand and quantify the hydrologic cycle and its spatial and temporal interactions with the natural and built environment. Just as in balancing a bank account, it is important to keep track of the amount of water in storage and the rates of inflow and outflow. Natural inflows to surface-water bodies typically include precipitation, surface runoff, and groundwater inflow; outflows include evaporation, transpiration, and seepage into the ground. Natural inflow to groundwater (recharge) results from the percolation of soil and other surface waters; outflows include transpiration and discharge to surface waters. Humans also withdraw from, and discharge to, surface and groundwater.

There are two main challenges to understanding and quantifying the movement of water between and within stores and the associated changes in water constituents. First, many of the key processes, such as evaporation or movement of groundwater within an aquifer, cannot be readily observed over large areas. Second, the rates of water movement can vary greatly in both space and time.

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Summary
Water in the right quality and quantity, and at the right time, is essential to
life—for humans and their food crops, and for ecosystems. Millions of people
yearly die of water-related diseases; floods and droughts also cause illness and
death in addition to economic damage throughout the world. Much of our agricul-
tural activity would collapse in the absence of irrigation water. Natural ecosystems
are adapted to stream discharge, precipitation, and evaporation patterns. Thus, future
adjustments in the water cycle to climate, weather, and land-use change will un-
doubtedly have complex and significant impacts on humans and other species that
depend on it.
THE CHALLENGE OF UNDERSTANDING WATER
FLOWS AND STORES
The management of water resources to meet these challenges will require
improvements in our capacity to understand and quantify the hydrologic cycle
and its spatial and temporal interactions with the natural and built environment.
Just as in balancing a bank account, it is important to keep track of the amount
of water in storage and the rates of inflow and outflow. Natural inflows to sur-
face-water bodies typically include precipitation, surface runoff, and groundwa-
ter inflow; outflows include evaporation, transpiration, and seepage into the
ground. Natural inflow to groundwater (recharge) results from the percolation
of soil and other surface waters; outflows include transpiration and discharge to
surface waters. Humans also withdraw from, and discharge to, surface and
groundwater.
There are two main challenges to understanding and quantifying the move-
ment of water between and within stores and the associated changes in water
constituents. First, many of the key processes, such as evaporation or movement
of groundwater within an aquifer, cannot be readily observed over large areas.
Second, the rates of water movement can vary greatly in both space and time.
1

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2 Integrating Multiscale Observations of U.S. Waters
Three strategies are used individually or in combination to get around these
problems, with varying degrees of success. First, when feasible, variables such as
precipitation, river discharge, and wind speed are measured at specific locations
(“point” measurements). Second, remote sensing methods can provide informa-
tion on the spatial distribution of key variables. These methods measure over large
areas, but the measurements represent averages over some space and time “win-
dow”. Remote sensing can be ground based (e.g., radar estimates of rainfall), or
based on aircraft or satellites. Third, models are used to interpolate between point
measurements (e.g., precipitation), estimate unmeasured quantities based on
measured ones (e.g., chlorophyll concentrations from certain wavelengths of light,
or evaporation from wind speed, temperature, and relative humidity) and to predict
hydrological conditions under a hypothetical future combination of land use, land
cover, and climate.
Even with these tools, the field suffers great limitations in many areas of
measurement. For example, for most aquifers there are no accurate estimates of
recharge, especially their spatial and temporal resolution. Likewise, accurate
measurements of the spatial distribution of snow water storage are virtually im-
possible to make in many areas due to extreme topography and/or limited ac-
cess.
THE PURPOSE OF THIS REPORT
Out of interest in these issues and their implications, in 2005 the National
Research Council’s (NRC) Water Science and Technology Board (WSTB)
formed the Committee on Integrated Observations for Hydrologic and Related
Sciences to examine the potential for integrating new and existing spaceborne
observations with complementary airborne and ground-based observations to
gain holistic understanding of hydrologic and related biogeochemical and eco-
logical processes and to help support water and related land resource manage-
ment. Funding for this effort (or for its parent standing committee, the Commit-
tee on Hydrologic Science [COHS]) was received from the National Aeronautics
and Space Administration (NASA), the National Science Foundation (NSF), the
U.S. Army Corps of Engineers (USACE), the National Oceanic and Atmos-
pheric Administration (NOAA), the Nuclear Regulatory Commission, and the
Environmental Protection Agency (EPA). The full Statement of Task is shown
in Box S-1. This report offers a comprehensive view of the current state of inte-
grated observing for hydrology and the related sciences, with a particular em-
phasis on sensing.

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Summary 3
BOX S-1
Statement of Task
This study will examine the potential for integrating new and existing
spaceborne observations with complementary airborne and ground-based obser-
vations to gain holistic understanding of hydrologic and related biogeochemical
and ecological processes and to help support water and related land resource
management. These systems are closely interconnected, and a great deal of
common information is required in their study. The goal is to focus on informa-
tion that would contribute to quantifying current and projected water availability,
water quality and biogeochemical cycling, and land-surface and related ecologic
conditions. The assessment would consider these goals in the light of the capa-
bilities of sensor and other in-situ monitoring technologies and of spaceborne
observation technologies. It would also look at likely advances in these tech-
nologies. The study will:
(1) Identify processes in water flow and transport, related biogeochemical
cycling, and ecological impacts where better information is needed to under-
stand important mechanisms, how systems integrate at watershed and larger
scales, and where new instrumentation or strategies for instrument placement
could supply the needed data;
(2) Identify contributions that observations obtained by remote sensing or
other existing technology could make to understanding water flow and transport
and related biogeochemical cycles as well as for addressing water management
activities such as agricultural and municipal water supply, flood and drought
prediction, water quality, and energy production;
(3) Evaluate the readiness of the scientific and technical communities to
make effective use of more precise and reliable observations of hydrologic
fluxes and states (e.g., soil moisture, snow cover, carbon and nutrient transport,
water bodies and wetlands, and water-quality indicators);
(4) Suggest research opportunities in these areas; and
(5) Identify gaps in federal agency plans for integrating across sensors and
products obtained from either in-situ or space-based observations.
OVERVIEW
The good news is that recent and potential future technological innovations
offer unprecedented possibilities to improve our capacity to observe, understand,
and manage hydrologic systems. Sensors are being developed that are smaller,
less expensive, and require less power, allowing for deployment in much larger
numbers. Researchers are designing sensors to provide previously unavailable

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4 Integrating Multiscale Observations of U.S. Waters
information, such as real-time measurements of nutrient concentrations in sur-
face, soil, or groundwater. Sensors are being arrayed in networks that enable the
sharing of information and hence produce synergistic gains in observational capac-
ity; these sensor networks offer the promise of filling critical gaps between tradi-
tional point and remotely sensed measurements. New sensors are being deployed
on aircraft and satellites, and new ways are being thought of to use existing remote
sensors. Computer models are being used to assimilate data from multiple sources
to predict system behavior. And cyberinfrastructure initiatives are providing effi-
cient and effective ways to share data with scientists, managers, and other potential
users.
But there are gaps between the vision of what researchers and managers
want to achieve and their ability to realize that vision. These gaps are real, but
in many cases extremely narrow. Technical challenges include those associated
with the development of robust, accurate, and affordable water-quality sensors.
All of the required technologies are expensive to develop, and most will at least
initially require public funding until their commercial viability is established.
Design and implementation of integrated hydrologic measurement systems re-
quires the cooperation of diverse sets of researchers, technologists, and deci-
sionmakers. How can this cooperation be facilitated? Water management in the
United States is typically local and rarely integrated. How can integrated hydro-
logic measurements provide greater benefit to local or regional decisionmaking?
A series of case studies was developed for the report, for regions as diverse
as the Arctic, sub-Saharan Africa, and the Everglades, as well as the Great
Plains, Mountain West, and coastal North Carolina of the United States.
• “Monitoring the Hydrology of the Everglades in South Florida” pro-
vides an example of a large, complex integrated observatory designed to address
pressing water management needs in an ecologically sensitive area.
• “Impacts of Agriculture on Water Resources: Tradeoffs between Water
Quantity and Quality in the Southern High Plains” focuses on semiarid regions
where water availability is a critical issue and where cycling of salts has large-
scale impacts on water quality.
• “Hydrological Observation Networks for Multidisciplinary Analysis: Wa-
ter and Malaria in Sub-Saharan Africa” illustrates how observations can contribute
to understanding and ameliorating major water-related public health problems.
• “Achieving Predictive Capabilities in Arctic Land-Surface Hydrology”
explores a strategy for robust remote sensing hydrology in the pan-Arctic, to iden-
tify capabilities needed to link in-situ observations to satellite sensor-scale obser-
vations.
• “Integrating Hydroclimate Variability and Water Quality in the Neuse
River (North Carolina, USA) Basin and Estuary” focuses on the impact of human
activity and hydroclimate variability on watershed nitrogen sources, cycling and
export, and consequently on fresh water and estuarine ecosystem health.

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Summary 5
• Finally, “Mountain Hydrology in the Western United States” discusses
the need for high spatio-temporal resolution information on snow conditions due
to sharp wet-dry seasonal transitions, complex topographic and landscape pat-
terns, steep gradients in temperature and precipitation with elevation, and high
interannual variability.
These case studies, taken in the context of discussions of sensors, networks,
communications, data assimilation, and modeling, illustrate a number of impor-
tant challenges regarding current and potential sensors and sensor networks,
merging the resulting information with models, and providing useful products to
managers and policymakers through traditional and emerging dissemination
media. These challenges are presented below.
CHALLENGES
Development and Field Deployment of Land-Based
Chemical and Biological Sensors
Physical sensors, such as those that measure air and water temperature and
pressure, radiation, and wind speed and direction, are now mass produced and
routinely packaged together in small instruments along with power and commu-
nication devices. However, sensor development for many important chemical
and biological measurements is relatively immature. Development of a wide
range of field-robust chemical and biological sensors is one of the greatest chal-
lenges facing widespread deployment of sensor networks in the hydrologic sci-
ences.
Airborne Sensors
Airborne measurements operate at a spatial scale that fills the gap between
the in-situ plot-scale observations and the larger satellite-scale observations.
Airborne remote sensing at NASA historically was viewed as an intermediate
step between initial sensor development and space deployment to help develop
retrieval algorithms to validate new satellite sensors. It has not been viewed as a
sensor program in its own right. This has impeded the development of opera-
tional airborne observing platforms that could play a very important role in hy-
drologic observations.
Spaceborne Sensors
In satellite-based remote sensing, NASA has made good progress in devel-
oping and deploying sensors used primarily for research. Nonetheless, two chal-

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6 Integrating Multiscale Observations of U.S. Waters
lenges are relevant to this report: (1) a resolution of the “research-to-operations”
transition from NASA-developed “experimental” satellite observations to the
broad variety of operational agencies and users that need routine (i.e., operational)
observations, and (2) the lack of a corresponding monitoring strategy by entities
such as EPA, USDA, NOAA, and state water and natural resources agencies that
would incorporate airborne and/or satellite remote sensing measurements, where
appropriate.
Bridging the Gap between Sensor Demonstration and
Integrated Field Demonstration
There are significant interagency gaps between the steps of sensor devel-
opment, sensor demonstration, integrated field demonstrations, and operational
deployment of sensors. The greatest gap is between sensor demonstration and
integrated field demonstration. Closing this gap would involve integrating the
sensor networks and webs within hydrologic observatories and experimental
demonstration sites, and interfacing the sensor networks with the broader devel-
opment of cyberinfrastructure.
Integrating Data and Models for Operational Use
The importance of data-model integration is apparent in a number of the
case studies. For the Mountain Hydrology study, predictions of water availabil-
ity are made from point measurements and model forecasts. In the Neuse River
Basin study, management decisions are based on sparse water-quality measure-
ments. In each case, models and observations are used to guide management
decisions, and in each case a data assimilation system that merges models and
observations would offer improved predictions. The challenge is to develop
methods that will be useful for broad families of applications, rather than just a
few of the many possible applications.
The Next Step: Water Resources Applications
In the United States, large water resources problems involve multiple stake-
holders, including government agencies, business interests, and the public. Man-
agement is typically diffuse, and standard measurement and modeling techniques
and rules for water management are entrenched and often legally mandated. This
produces a consistent data set to show trends over time, and simplifies training and
daily tasks of staff. However, it also leads to missed opportunities to improve the
accuracy and precision of the data and resulting model predictions.

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Summary 7
Funding Highly Interdisciplinary Science
Interdisciplinary science is increasingly common, but the design and use of
integrated hydrologic measurement systems in specific research applications adds
complexity to the challenge. These new kinds of projects will require unprece-
dented interdisciplinary cooperation among electrical engineers, computer scien-
tists, modelers, and the physical, chemical, and biological scientists who apply
technology to hydrologic research. While many universities and research labora-
tories have the required expertise, marshalling this expertise on specific projects
will likely require new programs or sources of funding.
Addressing the Fractured Federal Responsibility
for Hydrologic Measurement, Monitoring, and Modeling
The overarching barrier to the development and implementation of integrated
hydrologic measurement systems is the lack of a single federal agency with pri-
mary responsibility for measuring, monitoring, and modeling the environmental
factors and processes that control the hydrologic cycle. It is easy to understand
why the responsibility for measuring and monitoring the environmental factors
and processes that control the hydrologic cycle might have evolved as it has. But
the dual threats of global climate change and population growth demand a focused
strategy for providing information on the nation’s water resources and the envi-
ronment.
The above challenges, along with the body of the report, lead to the recom-
mendations of the study, which follow below.
RECOMMENDATIONS
Recommendation 1: NSF, in partnership with NASA, NOAA, EPA, U.S. Geo-
logical Survey, and possibly national health and security agencies, and with col-
laboration from the private sector, should develop one or more programs that
address the need for multidisciplinary sensor development. An interagency sen-
sor laboratory should be considered.
Recommendation 2: Serious consideration should be given to empowering an
existing federal agency with the responsibility for integrated measurement, moni-
toring, and modeling of the hydrological, biogeochemical, and other ecosystem-
related conditions and processes affecting our Nation’s water resources.
Recommendation 3: Coordinated and jointly funded opportunities for observa-
tories, demonstration projects, test beds, and field campaigns should be signifi-
cantly increased.

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8 Integrating Multiscale Observations of U.S. Waters
Recommendation 4: Agencies should consider offering new funding streams
for projects at the scale of several million dollars per year for approximately 5-
10 years to help close the gap between sensor demonstration and integrated field
demonstration.
Recommendation 5: NASA should strengthen its program in sensor technol-
ogy research and development, including piloted and unpiloted airborne sensor
deployment for testing new sensors and as a platform for collecting and trans-
mitting data useful for applications.
Recommendation 6: In addition to partnerships with other federal agencies for
the development and testing of experimental sensors that are of a particular in-
terest to agencies, the Nation, and especially NASA, should explore additional
strategic partnerships with space agencies in other countries and regions, such as
the European Space Agency (ESA), the Japanese Aerospace Exploration Agency
(JAXA), the Centre National d'Études Spatiales (France), and the Canadian
Space Agency (CSA).
Recommendation 7: NASA and NOAA should work with NSF and other agen-
cies to assure that plans for incorporation of space-based and airborne observations
(from both existing and, preferably, planned or proposed missions) are part and
parcel of the experimental design of these proposed observatories.
Recommendation 8: Advanced cyberinfrastructure should not only be incorpo-
rated as part of planned observatories and related initiatives to help manage,
understand, and use diverse data sets, but should be a central component in their
planning and design.
Recommendation 9: Utilization of web-based services, such as collaboratories
(i.e., web-based systems where researchers and users come together to build a
system of data, predictive models, and management projects), for the distribu-
tion of observations, model predictions, and related products to potential users,
should be encouraged.
Recommendation 10: NASA and NSF should develop and strengthen program
elements focused on demonstration projects and application of data assimilation
in operational settings where researchers work collaboratively with operational
agencies.
Recommendation 11: NASA should take the lead by expanding support for the
application of integrated satellite remote sensing data products. NSF, NOAA,
and other federal and state agencies engaged in environmental sensing should
likewise expand support for the creation of the integrated digital products that
meet educational, modeling, and decision-support needs.

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Summary 9
Recommendation 12: Congress, through the budgetary process, should de-
velop a strategy for transitioning NASA experimental satellite sensors to opera-
tional systems with assured data continuity so that the Nation’s investment in
remote sensing can be utilized over the long term by other federal agencies and
users.
Recommendation 13: Water agencies should be alert for opportunities to in-
corporate new sensor and modeling technologies that will allow them to better
deliver their mission and be more productive.

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